The biochemical relationships between thiadiazole, pyridine metabolism and the various antiteratogens to thiadiazole will be investigated in the rat embryo. Initially studies will be conducted to determine the effect of thiadiazole on the pyridine nucleotide coenzymes nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate. Studies will be conducted to determine the biochemical changes in the heart and limbs of rat embryos following teratogen treatment. To be studied are DNA and protein synthesis, mucopolysaccharide synthesis and the ontogeny of certain isoenzymes.